Light-emitting diodes (LEDs) are nowadays used in many cases for lighting purposes. Since LEDs typically generate narrowband, single-colored light having a quasi-monochromatic spectrum, a plurality of different-colored LEDs or one or a plurality of LEDs having an additional wavelength-converting dye have to be combined in order to generate white light.
A customary combination of LEDs for generating white light comprises quasi-monochromatic red LEDs having a peak wavelength in the range of approximately 600 to 700 nm, quasi-monochromatic green LEDs having a peak wavelength in the range of approximately 530 to 570 nm and quasi-monochromatic blue LEDs having a peak wavelength in the range of approximately 440 to 475 nm. If appropriate, LEDs having further colors can also be added to this so-called RGB combination.
Furthermore, it is also known, in a so-called RBW combination, to combine the abovementioned red and blue LEDs with one or a plurality of white-converted blue LEDs which generate blue light and have a dye that is excited by part of the blue light to emit light having longer wavelengths, which, in superimposition with the unconverted part of the blue light of the LED, produces white light.
By varying the light intensities respectively emitted by the individual LEDs, it is possible to generate different-colored mixed light, for example, also white light having different color temperatures. In this case, however, the individual LEDs are usually operated with low intensities depending on the mixed color to be obtained, as a result of which the total intensity of the mixed light is low. In order to achieve a certain luminous flux, it may be necessary as a result to use a larger number of LEDs, as a result of which the total costs for the LEDs increase.
It is also known to combine at least two or more white-converted LEDs each having a color locus lying on or near the white curve of a Planckian black-body radiator. In this case, the color loci and the white curve relate to the known CIE 1931 colorimetric diagram or CIE standard chromaticity diagram. In the case of such a combination with white-converted LEDs, however, it can happen that the superimposition of the white light respectively emitted itself does not lie on the white curve or at least regions on the white curve cannot be attained, particularly if only two different white-emitting LEDs or LED groups are used.